Electrolyzing indium oxide in fused caustic electrolyte



. Sept. 5, 1950 Solid 5 M. F. W. HEBE'RLEIN ETAL- ELECTROLYZING INDIUM OXIDE IN FUSED CAUSTIC ELECTROLYTE Filed Nov. 6, 1945 Fused Sodiuh Hydrox (Na OH) Ele-crrolysis (Fe. Elech odes) I J J,

F eni Elech olyie Jr Indium Mei'cll (WifhNcL,

ide

Fzn efc) (No In 0 No OH, N0 O,Fe,Zn dc l ionsand Mefallic' In Prflls KeH'le Refininq Wafer Leach (Hoi' Wc|feF) Mew H'c I No In O2,Nc| OH) separolror A In Finns Fe,Zn erc. ions 1 Merollic In PriHs CoKe Soluiion In (OH)3 Refined M r l Discard In Rerurn +0 Nurrcl Leach of Heberle'm Uclin Process Max Kai INVENTORS.

MAX F. W. HEBERLEIN Y NEVIN R. BIERLV.'

Patented Sept. 5, 1?50 iii? ELECTROLY ZING-IND OXIDE IN FUSED QAUSTIC ELECTROLYTE 'Max F. W. Heberlein, Rahway, and Nevin R. Bierly, Avenel, N. J .,fassignors to The American Metal Company, Limited, New corporation of New York York, N. Y., a

Application November 6, 1945; Serial No. 627,014

Y This invention relates to electrolysis ofindium ina fused caustic electrolyte.

.- We have found that the usual methods em ployed for the reduction of other metal oxides are not satisfactory when applied to indium recovery. Tests with several carbonaceous reducing agents gave varying low yields as compared with yields of the process herein described.

The principal object of the invention is to provide a simple, efiicient process for recovering indium from indium material by electrolysis employing a fused caustic electrolyte. More particularly, the object of the invention is to provide a simple and eflicient process for electrolyzing indium oxide obtained by the practice of the Heberlein (co-inventor of this application) and Udin process disclosed in their copending applicatio Serial No, 622,022, filed October 12, 1945. Other objects of the invention will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists of the novel processes and steps of processes, specificembodiinents of which are described hereinafter by way of example and in accordance'with which we now prefer to practice the invention.

In accordance with our invention, indium oxide is reduced to metal by electrolysis in fused caustic alkali. such as sodium hydroxide. Our method-has the particular advantage that it may be practised with substantially little or no metal losses. The electrolysis is preferably performed in a steel vessel serving as cathode and which may be heated externally. The anode is suspended in the center, preferably, and consists or a steel strip about thick by 4" wide and about 6" long. The reduced indium metal collects 'as a molten pool at the bottom of the vessel and can be tapped periodically through an outlet provided for this purpose.

The operation of the electrolysis is conducted in the following manner in accordance with our invention. A flow sheet forming part of the application shows the steps employed.

Sodium hydroxide flakes are melted down in the steel vessel, whereupon the indium oxide (111203) is added to the mass. Electrolysis is conducted with a current of about 400 amperes. Under this condition, about 300 grams of indium oxide (InzOa) are consumed per hour, the indium being liberated to the molten pool at the bottom of the cell as mentioned.

The temperature of the fused caustic sodaindium oxide bath should preferably be about 800 F. and during the electrolysis the tempera ture range should be maintained at about the 7 Claims. (01.20971) tained should be about 2.5 to 7 .amperes pert square inch of anode surface.- H

In the operation of'electrolysis, very little ex-i ternal heating is necessary becausemost of the heat required to keep the electrolyte molten once':

it is brought within the heating range is supplied by the electric current.

I Indium oxide is periodically stirred into the 1 electrolyte during the run. Although iron orsteel is highly resistant to the corrosive attack of fused caustic soda, the electrolyte dissolves a" considerable amount of both the anode and the cathode. During the electrolysis, sodium oxide (NazO) tends to build up. This material does not melt-"below its sublimation temperature of 1275 C. (232'7 F.). It reacts very slowly with water or steam at the operating temperature of the cell and for this reason it can not be readily reconverted to sodium hydroxide during the elec-*' trolysis. For this reason it is considered preferable to discard the electrolyte every 48 hours, employing the above-sized apparatus, and to con-- tinue with a new batch of sodium hydroxide. The discarded electrolyte mixture of sodium hydroxide and sodium oxide was found to contain up to about 3% iron and up to approximately 7 indium.

Since the indium oxide is dissolved in the caustic soda as Nazolnzos, or NaInOz, metallic so-' dium is deposited at the cathode and IiiaOa must be liberated at the anode. The reduction of the InzOa is then brought about according to the following equation:

Some metallic sodium escapes this reaction, al-

. timony, thallium and bismuth, and the balance indium. This material is melteddown in the kettle and the sodium is removed completely by pouring water onto the surface of the molten metal. Caustic soda forms and is skimmed off, Themetal is then heated to about'600 F. and; treated with caustic soda, watenandniter for:

order of 750-850 1. The current density main;

the elimination of zinc and iron. Copper and a portion of tin are also removed with this treatment.

The caustic soda slag, together with the dross obtained by the above treatment with caustic soda, watuand niter for the elimination'of zinc and iron, arecombined with thespent electrolyte. This material is then leached in hot water to separate the insoluble In(OH)3, indium hydroxide,

and the metallic indium prills. While the metallic prills are combined with the metal produced in the electrolytic cell, the indium oxide is returned to the operation for recovering indium and other values by combining it with the water leach residue to be supplied to the neutral leach,

4 was removed and replaced by a batch of 18.5 kgs'. of fresh fused sodium hydroxide.

The electrolyte mixture of sodium hydroxidesodium oxide containing up to 3% iron and up to approximately 7 indium upon removal from the cell was .then leached in hot water to separate the, insoluble indium hydroxide In(OI-I)3 and metallic indium prills. The metallic prills were combined with the metal produced in the elecdisclosed in the said copending application of Max F. W. Heberlein and Harry Udin. This indium hydroxide contains also other impurities such as iron and zinc, together with copper and About 18 5 kgs. of commercial sodium hydroxide flakes were melted down in a steel vessel of about '1 xl-":x1.2" depth serving. as a cathode which may be heated externally. This quantity oi austic soda. gives. a. bath. d pth of appr x 1 0,inches. Aboutlfikgs. of indium oxide (1221203.)- contain'ing a littleZnO are added to the molten bath and the, temperature of. the fused caustic soda-indium. oxide bath is, adjusted toabout. 8 003 A steel. strip. anode was then inserted in he molten, bath. The steel anode. consisted of. a strip. about, A thichand 4-" wide- Itwas. submerged in the center of the cell to about i 4 inches from, the bottom. Current of 400. am-

peres. was. used, giving acruiren-t density. of about. 'l amperes, per square inch; anode surface. The. fimpera'tureof thebath was maintainedat about. 7 50 85 0? E. Theinitial. cell voltage was. approxl mately volts. After about 48 hoursit. increased to nearly 7.5 volts. Most of the heat required to keep the eleotrolytemolten was. supplied by the current. About, 1.50. grams. of, indium oxide; 1112.03). were. added every half hour. Larger quantities tended to thicken the. electrolyte too; much. forsmcoth operation. inthe, particular apparatus. employed, Under this. condition! about, 300 grams ImlQa, were consumedper. hour... reduced. indium. metal, an alloy of indium and sodium. melting, at. 725,- '0 FL, collected asZ a. moltcnpool 'inthebottom and'was tapped periodi callyfroman outlet provided. for "that purpose.

Durin 'the'ccurse of. the electrolysis, sodium oxid (NazO). which does not meltbelow the. sub! limation temperature of 127.5 C. (2327..F.),.CQ1{- lects in thecell. Ltreacts very slowly with. water. at, the operating temperaturesof the: celland "f r; thisreason it was not convertedjto. caus ic sodaduring. the electrolysis... At the end. off-eyery (hours the electrolyte, which. had. built.- urpa wtainquantity ofironandsodiunr oxide.

trolytic cell, the indium hydroxide being returned to the operation by combining it with the residue resulting from the acid leach of the water leach residue as described in the copending application of Max F. W. Heberlein and Harry Udin, Serial No. 622,022, filed October 12, 1945. following shows the metal balance of a run of The 48 hours using the single cell operation described:

Kgs. InzOs charged to cell 14.0 In content of charge 11.2 In-content of spent electrolyte 2.1 Metal tapped from cell 9.0 Loss 0.1

The metal taped from the cell was remelted in a gas-fired steel kettle for a final refining treatment. Spectrographic analysis of the metal tapped from the cell is shown in the following:

Pb .05% Zn High 0.5% Sn- 114% Tl Trace Sb Trace Cd .0059! Cu .005-;02'% Na High 1.0% Fe; -.02-.04'% In Balance Bi Trace This material is melted in the kettle and .the sodium is removed completely by water poured onto the surface of the molten metal. A viscous caustic soda slag forms and can be easily skimmed on. The metal is then heated to about '60'0 F. and treated with caustic soda, water and niter (Na'NOzg) for the elimination of zinc and iron as oxides. Atypical assay of the refined metal shows" the following impurities:

Trace The kettle dross; resulting from the above is. combinedwithhot -spent electrolyte and leached in hot water.. The residue consistingmostly of indium hydroxide is returned to the neutral leachvopcration ofthe Heberlein and- Udin proc essv mentioned above- Example 2 About 18.5 kgs. of commercial sodium .hydroxride. flakes. were charged into each of two steel cells connected electrolytically in series-,, thedimensionsof. the. cells. being substantially those mentioned iniExample 1. To each ofthe molten bathsin. these cellsnvas. added 1.5 kgs...of. indium" oxide. (11120;) contam'im;alittle ZnO and the.

temperature of the fused caustic soda-indium oxide bath is adjusted in each cell to about 809 F. A steel strip of the dimensions given in Example 1 was inserted in each cell in the manner described in Example 1. Electroylsis was conducted employing a current of about 400 amperes and a current density of about 7 amperes per square inch of anode surface. The operation was conducted for 48 hours in substantially the same manner as that in Example 1 and the results are shown in the following metal balance:

Kgs.

InzOs charged to cell 27.8

In-content of charge 22.2

In-content of spent electrolyte 5.8

Metal tapped from 2 cells 16.3

Loss 0.1

We claim:

1. The process which essentially comprises, electrolyzing indium oxide (InzOs) containing iron as impurity dissolved in molten sodium hydroxide at a temperature of about 750-850 F. to produce impure indium metal, thereby building up the content of sodium oxide and iron in the electrolyte, and recovering said impure indium metal.

2. The process which essentially comprises electrolyzing indium oxide (InzOa) dissolved in molten caustic alkali to form a sodium-indium alloy, maintaining the temperature of the bath at a point where the alloy collects as a molten mass, removing the alloy, and recovering the indium.

3. The process which essentially comprises electrolyzing indium oxide (In2Os) dissolved in molten sodium hydroxide to form a sodium-indium alloy, using as electrodes a metal of a high melting point, maintaining the temperature of the bath at a point where the alloy collects as a molten mass, removing the alloy, and recovering the indium.

4. The process which essentially comprises electrolyzing indium oxide (InzOa) dissolved in molten caustic alkali to form a sodium-indium alloy, using steel electrodes, maintaining the temperature of the bath at 750-850 F., removing the alloy, and recovering the indium.

5. The process which essentially comprises electrolyzing indium oxide (InzOa) dissolved in molten sodium hydroxide to form a sodium-indium alloy, maintaining the temperature of the bath at a point where the alloy collects as a molten mass, adding water to said alloy, and removing a dross containing sodium hydroxide.

6. The process which essentially comprises electrolyzing indium oxide (InzOs) dissolved in molten caustic soda to form a sodium-indium alloy containing small amounts of sodium, iron and zinc, adding Water to the alloy, removing a dross containing sodium hydroxide, treating the resultant metal after removal of the sodium hydroxide with niter, sodium hydroxide and water to form a dross containing iron and zinc and removing the last-mentioned dross.

7. The process which essentially comprises electrolyzing indium oxide (InzOs) containing iron and zinc as impurities dissolved in molten sodium hydroxide at a temperature of about 750-850 F. to form a pool of impure indium metal containing sodium, iron and zinc, removing spent electrolyte when the iron content thereof reaches about 3%, oxidizing sodium, iron and zinc contained in the impure metal, removing such oxidized metals from said indium metal, and recovering indium values from the spent electrolyte and said oxidized metals.

MAX F. W. I-lIEBERLEIN. NEVIN R. BIERLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 785,962 Lyons et al. Mar. 28, 1905 1,338,279 Blumenberg Apr. 27, 1928 2,238,437 Zischkau Apr. 15, 1941 2,241,438 Zischkau et al. May 13, 1941 2,384,610 Doran et al. Sept. 11, 1945 FOREIGN PATENTS Number Country Date 163,812 France Aug. 18, 1884 OTHER REFERENCES Comptes Rendus, vol. 190 (1930), pages 925- 927.

Metal Finishing, July 1944, page 406.

Transactions of The Electrochemical Society, vol. (1944), pages 223, 224. 

1. THE PROCESS WHICH ESSENTIALLY COMPRISES, ELECTROLYZING INDIUM OXIDE (IN2O3) CONTAINING IRON AS IMPURITY DISSOLVED IN MOLTEN SODIUM HYDROXIDE AT A TEMPERATURE OF ABOUT 750-850* F. TO PRODUCE IMPURE INDIUM METAL, THEREBY BUILDING UP THE CONTENT OF SODIUM OXIDE AND IRON IN THE ELECTROLYTE, AND RECOVERING SAID IMPURE INDIUM METAL. 